You can build your very own small pond in your yard over the course of a single weekend. A small koi pond or water garden can add visual interest to your outdoor space and studies even show that keeping fish can help you to reduce stress. Just make sure that if you have very small children, you build a fence around your pond to keep the kids safe.
Start by digging out a hole for your pond. You are going to need at least 40 square feet, or about seven feet by four feet, for the water to stay clean. If you want to add fish, you may need even more space. Check with an aquarium store employee for how big and deep you need to make your pond for the amount of fish you want to keep; koi require a depth of at least three feet, but you can keep goldfish in half that space. If you live somewhere where it snows, you will need to slope your pond's edges to keep the ice from expanding outward in the winter. Line the floor of your pond with sand so that any exposed roots or sharp objects are covered. Top this layer of sand with a pond liner, which you can buy at any aquarium store and some home and garden centers.
Fill your pond with water from your hose and install a pump, filter and waterfall. The waterfall is optional and just for looks, but the pump and filter are necessary to keep the water clean and moving so that you don't kill your plants or fish or attract unwanted mosquitos. Turn on your pump and allow the water to sit in your pond for at least 24 hours. The following day, you can add aquatic plants and fish to your pond. Don't add any fish right away, or you risk shocking them with chlorine from your water.